For changes in the questionnaires: See Chapter 3 on ‘Content of NIS Questionnaires’ in the Data User’s Guide (1995-2001).
For changes in the data editing procedures: See Chapter 4, section on ‘Limitations of Data Editing Procedures’ in the Data User’s Guide (1995-2001); some provider-data editing procedures were not implemented in 1995-2001 NIS.
Changes in the estimation procedure: For 1998, a new estimation procedure was implemented to obtain vaccination coverage rates from the provider data. For consistency, this procedure was applied to the NIS data for the years 1995-1997, and the resulting estimates are published on the NIS Web site. Published estimates of vaccination coverage based on NIS data for years prior to 1998 (e.g., estimates published in MMWR articles) may differ slightly from the estimates published on the NIS Web site for the same NIS data. All Public-Use Data Files include the sampling weight (W0) for the new estimation procedure. See Chapter 6, section on ‘Adjustment for Provider Nonresponse’ in the Data User’s Guide (1995-2001).